A number of resin compositions have been developed for use in a variety of applications. As described later, propylene-based resin compositions are employed for some applications, but further improvements are requested on the properties required in each application.
For instance, various materials have been used in components or parts and sheets for automobile components, industrial machine components, electrical and electronic components, building materials, and cap liners where rubber elasticity is required. An example of such material is vulcanized rubber. Vulcanized rubber is generally produced by kneading rubber with crosslinkers, crosslinking auxiliaries, additives, auxiliaries, and others to prepare an unvulcanized rubber blend, followed by vulcanization with heating. Therefore, vulcanized rubber encounters problems of complicated production processes and a high cost. In addition, due to thermosetting nature, vulcanized rubber cannot be recycled.
On the other hand, vinyl chloride resin is known as a material that does not require vulcanization but has rubber-like properties. However, vinyl chloride resin is inferior in rubber elasticity to vulcanized rubber, resulting in limited application. Recently, development of a material substituting vinyl chloride resin has been awaited for reasons such as the difficulty in incineration.
A thermoplastic elastomer is known as a polymer material that is plasticized and moldable like plastics at high temperatures while exhibiting rubber elasticity at normal temperature. As a recyclable olefinic thermoplastic elastomer, a dynamically crosslinked product of polypropylene and ethylene/α-olefin copolymer is known. However, in this case, there is also a problem of an increased cost due to the need of using crosslinkers and crosslinking auxiliaries.
In order to overcome these shortcomings, Patent Document 1 proposes a polyethylene-based resin composition mainly composed of an olefinic elastomer mainly derived from ethylene and its use. However, the heat resistance is insufficient because the major component is polyethylene.
As another measure, compositions comprising propylene-based polymers have recently been studied (see Patent Document 2).
However, the composition in Patent Document 2 still has room for improvement in mechanical properties, oil acceptance, or others. In addition, neither rubber elasticity nor permanent compression set at high temperature is described in Patent Document 2.
On the other hand, as described above, a thermoplastic elastomer is known as a polymer material that is plasticized and moldable like plastics at high temperatures while exhibiting rubber elasticity at normal temperature. Examples thereof include, besides the dynamically crosslinked product of polypropylene and ethylene/α-olefin copolymer, a composition of polypropylene and a styrene-based elastomer (see Patent Document 3). This material is excellent in strength, flexibility, and heat resistance, and hence, can suitably be used for cap liners and others.
A thermoplastic olefinic elastomer comprising polypropylene and ethylene/α-olefin copolymer is also used because flexibility can be further improved (see Patent Document 4).
However, the above olefinic thermoplastic elastomers are insufficient in balance of flexibility and scratch resistance, causing a problem that scratch resistance and whitening resistance are deteriorated if sufficient flexibility is attained. These are the background art for the first and second aspects of the present invention.
Polypropylene-based resin compositions are used in various applications such as electrical and electronic components, industrial materials, furniture, stationery, convenience goods, containers and packages, toys, leisure goods, and medical articles because of their excellent heat resistance, transparency, and moldability. As a technology of improving the flexibility and impact resistance of polypropylene-based resin compositions, addition of various soft materials is also known.
For instance, Patent Document 5 describes that a composition composed of a polypropylene-based resin and a specific propylene/ethylene/α-olefin copolymer elastomer is excellent in transparency and usable, for example, for stretch films.
Patent Document 6 describes a composition composed of polypropylene and a specific α-olefin copolymer elastomer in which the propylene content is more than 20 wt % and not more than 80 wt %, the ethylene content is more than 10 wt % and not more than 45 wt %, and the α-olefin content is more than 10 wt % and not more than 45 wt %.
Patent Document 7 describes a composition composed of polypropylene and a specific propylene/butene/ethylene copolymer is usable for industrial shrink films and wrap films for service.
Patent Document 8 describes, for example, that a composition composed of amorphous propylene/butene random copolymer and crystalline propylene-based polymer is excellent in whitening resistance on folding and usable for molded articles, transparent boxes, and others.
Patent Document 9 describes a sheet excellent in whitening resistance and transparency made of a composition mainly composed of a styrene-based elastomer and polypropylene.
When polypropylene is used in applications where transparency is required, such as stretch films, the film is sometimes required to maintain transparency when stretched or after treated at high temperatures.
However, the compositions in Patent Documents 5 and 6 are insufficient in whitening resistance on stretching or heating. Further, the compositions in Patent Documents 7 and 8 are poor in strength and have difficulties in practical use.
The composition comprising the styrene-based elastomer described in Patent Document 9 is excellent in whitening resistance, flexibility, and transparency, but styrene-based elastomers are generally immiscible with polypropylene, whereby molded articles of such composition are whitened under some service conditions. Moreover, the composition containing the styrene-based elastomer has excellent rubber elasticity at room temperature, but its rubber elasticity is poor at high temperatures. These are the background art for the third aspect of the present invention.
As a material widely used for heat-shrinkable films, polyvinylchloride resin and polystyrene resin are known. There is, however, concern about adverse effects on human bodies and environment of byproducts generated on disposal of these resins. Therefore, development of heat-shrinkable films using polyolefin is now underway. Conventional heat-shrinkable films made of polyolefin-based resin are inferior to heat-shrinkable films made of vinyl chloride resin in mechanical strength and heat shrink ratio at low temperatures. In particular, when this film is used as heat-shrinkable labels for beverage PET bottles, the film is often subjected to shrinking process together with a PET bottle in a heat-shrink tunnel using steam or others, and therefore, there is demand for a heat-shrinkable film having a high shrink ratio at lower temperatures.
Further, for separating PET bottles and label resins on recycling PET bottles, PET bottles and label resins are pulverized together and gravitationally separated in liquid phase based on the difference between these materials in buoyancy in water. For example, the specific gravity of polystyrene-based resin is about 1.03 to about 1.06, so that polystyrene-based resin sinks in water together with PET resin, which has a specific gravity of 1.3 to 1.5. Therefore, the label made of such resin having a specific gravity of 1 or higher is difficult to separate from PET resin by the above method. For this reason, a low-temperature heat-shrinkable film made of polyolefin having a specific gravity smaller than 1 is awaited to be developed.
As an attempt to meet this demand, for example, Patent Document 10 discloses a heat-shrinkable film obtained from crystalline polypropylene and propylene/1-butene random copolymer. This film has a high heat shrink ratio and is excellent in transparency. However, since the propylene/1-butene random copolymer (optionally containing 10 mol % or less of another α-olefin unit) is poor in impact resistance, the film obtained from this copolymer is also insufficient in flexibility or impact resistance.
Patent Document 11 discloses a heat-shrinkable film made of propylene/α-olefin random copolymer and petroleum resin wherein the copolymer is obtained from propylene and a C2-C20 α-olefin and has a melting point of 40 to 115° C. as measured with a DSC. This film possesses a higher heat shrink ratio than the film in Patent Document 10, but it is still insufficient in flexibility and impact resistance.
Patent Document 12 discloses a heat-shrinkable film having a film mainly composed of a propylene/α-olefin random copolymer (propylene/ethylene random copolymer) as an intermediate layer.
In the propylene/α-olefin random copolymer, 2 to 7 mol % of a co-monomer (ethylene or α-olefin) is copolymerized with propylene. The propylene/α-olefin random copolymer (propylene/ethylene random copolymer) alone cannot attain a sufficient heat shrink ratio, and impact resistance of films obtained therefrom is also poor.
Patent Document 12 also discloses a technology of adding linear low-density polyethylene and ethylene-based rubber to a propylene/α-olefin random copolymer (propylene/ethylene random copolymer). This technology improves heat shrink ratio and impact resistance of the film, but has a problem that film transparency is lowered.
Patent Document 13 discloses that a composition consisting of 20 to 50 parts by weight of polypropylene and 80 to 50 parts by weight of propylene/butene/ethylene copolymer is usable for stretch films and others. However, the document does not describe film drawing or use for heat-shrinkable films. These are the background art for the fourth aspect of the invention.
As a sheet for surface decoration or protection in building materials, home electric appliances, automobile interior and exterior materials, and others, there have conventionally been used films mainly composed of vinyl chloride resin, which have well-balanced scratch resistance, whitening resistance on folding, wrinkle resistance, transparency, and others.
However, since such films have disadvantages such as difficulty in incineration as described above, a focus has been made in the art on polyolefin-based materials with less burden on environment.
For instance, Patent Document 14 discloses a decorative sheet having a polypropylene film as an essential component layer. Patent Document 15 discloses a decorative sheet having a thermoplastic olefinic elastomer as an essential component layer.
However, in the decorative sheet proposed in Patent Document 14, which has a polypropylene film as a component layer, the high crystallinity and the melting point of polypropylene cause problems such as lowering in flexibility and occurrence of cracks or whitening at bended faces during folding processing. The decorative sheet proposed in Patent Document 15, which has a thermoplastic-olefinic elastomer as a component layer, is excellent in flexibility and hardly encounters cracking or whitening at bended faces, but has problems of insufficient transparency and mechanical strength, and others.
In order to solve these problems, Patent Document 16 proposes a decorative sheet having a layer made of a resin composition containing a specific non-crystalline polyolefin and a crystalline polypropylene at a specific ratio.
This decorative sheet was less liable to cracks and whitening at bended faces but insufficient in mechanical strength, scratch resistance, and heat resistance.
Patent Document 17 proposes a decorative sheet having a polyester film as a surface protective layer.
Using a polyester film as a surface protective layer significantly improved mechanical strength and scratch resistance, but such material containing a polar group in its molecular chain had a problem of poor water resistance (resistance against water vapor permeation). These are the background art for the fifth aspect of the invention.
Polypropylene-based resin is a more excellent material than polyethylene-based resin (polyethylene-based elastomer) in heat resistance, mechanical resistance, and scratch resistance, and molded articles obtained from polypropylene-based resin are used in various applications. Molded articles prepared from a conventional polypropylene and inorganic filler are excellent in heat resistance and mechanical strength, but poor in flexibility and impact resistance. For this reason, in uses where such properties as flexibility and impact resistance are required, polyethylene-based resin is mainly employed. However, the problem is that molded articles of polyethylene-based resin are insufficient in scratch resistance.
As a molded article obtained from polypropylene-based resin and inorganic filler (flame retardant), an electric cable or wire harness is known, which requires scratch resistance. Patent Document 18 discloses an insulated electrical wire for automobiles using a specific propylene polymer. The molded article used in Patent Document 18 was excellent in flexibility and impact resistance but insufficient in scratch resistance. These are background art for the sixth aspect of the invention.
As a resin material having a low specific gravity, which means light in weight, and is excellent in flexibility and mechanical strength, a crosslinked foam is widely used in building interior and exterior materials, automobile components such as interior materials and door glassruns, packaging materials, convenience goods, and others. This is because, while mechanical strength of a resin is lowered when merely foamed for reducing its weight, foaming with crosslinking can attain weight reduction without lowering mechanical strength by bonding the molecular chains to each other through crosslinking reaction of the resin.
Crosslinked foams of resins are also used for footwear and footwear components, for example, shoe soles (mainly mid-soles) for sports shoes and others. This results from demand for a material that is lightweight, less deformed in long-term use, mechanically strong enough to be durable in use under severe conditions, low resilient so as to absorb impact on landing, and scratch resistance.
Conventionally, a crosslinked foam formed from ethylene/vinyl acetate copolymer has been widely used for shoe soles. However, the crosslinked foam formed from ethylene/vinyl acetate copolymer composition has a high specific gravity and a large permanent compression set. Therefore, when the foam is used for shoe soles, there are problems of heavy weight and significant abrasion caused by loss of mechanical strength due to compression during long-term use.
To overcome these disadvantages, Patent Documents 19 and 20 disclose a crosslinked foam obtained from ethylene/α-olefin copolymer and a crosslinked foam obtained from a mixture of ethylene/vinyl acetate copolymer and ethylene/α-olefin copolymer, respectively. In these foams, the specific gravity and permanent compression set are reduced, but satisfactory performances have not been attained.
As a material obtained by dynamic crosslinking of olefinic rubber, a thermoplastic elastomer is known (see Patent Document 21). However, Patent Document 21 does not suggest foaming. In addition, it is difficult to foam the thermoplastic olefinic elastomer at a high foaming ratio for providing foams with a low specific gravity. Therefore, the thermoplastic olefinic elastomer is not suitable for the above applications.
As described above, it has been hard to obtain foams having low specific gravity, low permanent compression set (CS), excellent tear strength, low resilience, and good scratch resistance. These are the background art for the seventh aspect of the invention.
Since films or sheets of soft polypropylene-based resin are superior to those of soft polyethylene-based resin in heat resistance, flexibility, and mechanical strength, it is expected that their use will be developed in automobile components, building materials, food industry, and others. In these fields, the film or sheet is used as laminates with inorganic material, such as metal (including aluminum, copper, iron, stainless steel, etc.) and glass, or various plastics in many cases, so that the film or sheet is required to have excellent adhesion to various materials. In particular, soft polypropylene-based resin that exhibits adhesion to inorganic materials such as metal has been awaited.
It is difficult to graft polypropylene-based resin with a polar monomer using an organic peroxide or the like, and such grafting greatly decreases the molecular weight, significantly lowering heat resistance and mechanical properties.
Patent Document 22 describes a technology of adding an organosilicon compound to polypropylene for improving adhesion to metal and others. However, the laminate obtained using this technology is poor in transparency, flexibility, and rubber elasticity, and hence, its use is limited. The polyethylene resin obtained by this technology has improved adhesion as compared with conventional unmodified polypropylene. However, the polypropylene-based resin obtained by this technology had high crystallinity, and therefore, it was sometimes easily peeled off since peeling stress was concentrated when peeling. These are the background art of the eighth aspect of the invention.
In conventional sheets for sealing a solar cell between front and back plates or sheets made of glass, plastics, or others (solar cell-sealing sheet), ethylene/vinyl acetate copolymer (in this specification, often abbreviated as “EVA”) has been commonly used. This is because EVA is flexible and highly transparent and provides long-term durability when blended with appropriate additives such as a weathering stabilizer and an adhesion promoter.
However, EVA has a low melting point, causing problems in heat resistance such as thermal deformation at environmental temperatures where solar cell modules are used. To resolve this problem, a crosslinked structure is formed by adding an organic peroxide to impart heat resistance.
Solar cell-sealing sheets are prepared by a known sheet molding process applicable to molding polyolefin. There has been a problem that addition of an organic peroxide disables high-speed production because low-temperature molding is inevitable to avoid decomposition of the organic peroxide.
The production process of a solar cell module configured as (glass or plastics)/(solar cell-sealing sheet)/(solar cell)/(solar cell-sealing sheet)/(back sheet) generally includes two steps: a temporary bonding step by vacuum heat lamination and a crosslinking step using a high-temperature oven. Since the crosslinking step using the organic peroxide takes several tens of minutes, omitting or speed-up of the crosslinking step is strongly required.
In long-term use of solar cells, gas generated by decomposition of EVA (acetic acid gas) or the vinyl acetate group in EVA itself may have adverse effects on the solar cell and lower its power generation efficiency.
To resolve such problems, a solar cell-sealing sheet using ethylene/α-olefin copolymer has been proposed (see Patent Document 23). With the proposed materials, the adverse effects on solar cell elements are considered to decrease, but balance of heat resistance and flexibility is insufficient. Furthermore, the crosslinking is hard to omit since desirable heat resistance is not attained without crosslinking. These are the background art for the ninth aspect of the invention.
Recent advancement in electrical/electronics elements is remarkable, and they have been widely used in every aspect of social, industrial, and domestic circumstances. Generally, electrical/electronics elements are easily affected by moisture, oxidants, and others, and hence, they are sealed in many applications to attain stable operation and long service life.
Nowadays, various materials for sealing electrical/electronics elements are produced and supplied in the market. Among them, a sealing sheet made of an organic polymer is very useful because of its applicability to relatively wide area and ease in use. In addition, transparency can be attained relatively easily, and hence, the sealing sheet is particularly suitable for sealing electrical/electronics elements using light, especially solar cells.
Solar cells are generally used in sealed solar cell modules, because they are used outdoors such as on the roof of buildings in many cases. The solar cell module has a structure in which a solar cell element made of polycrystalline silicon or others is sandwiched between solar cell-sealing materials made of a soft transparent resin to form a stack, of which the front and back surfaces are covered with solar cell module protective sheets. That is, a typical solar cell module has a layered structure, solar cell module protective sheet (front protective sheet)/solar cell-sealing sheet/solar cell element/solar cell-sealing sheet/solar cell module protective sheet (back protective sheet). Owing to this structure, the solar cell module has weatherability and is suitable for use outdoors such as on the roof of buildings.
As a material forming the solar cell-sealing sheet (solar cell-sealing material), ethylene-vinyl acetate copolymer (EVA) has been widely used from the viewpoint of transparency, flexibility, or others as described above (for example, see Patent Document 24). When used as the solar cell-sealing material, EVA is generally crosslinked to attain heat resistance. However, the crosslinking takes a relatively long time of about one to two hours, lowering the production speed and productivity of solar cell elements. Further, there has been a concern about possible adverse effects of acetic acid gas or other chemicals generated by decomposition of EVA on solar cell modules.
As one of the methods for solving the above-mentioned technical problems, use of a solar cell-sealing sheet made of non-crosslinked resin has been proposed (for example, see Patent Document 25). However, with an increase in requested levels of the productivity, durability under severe conditions, and service life of solar cells, all of the transparency, heat resistance, and flexibility have become required to have levels higher than those attainable with EAA, EMAA, or other resins proposed specifically in Patent Document 25. If such a request is satisfied, the sealing sheet would be quite useful for electrical/electronics elements besides solar cells.
When the sealing sheet is used for solar cell modules and others, since the sheet is laminated with glass or others in many cases, adhesion to glass and others is practically important. Some conventional sealing sheets have insufficient adhesion to glass and others, and hence, the improvement has been strongly desired. These are the background art for the tenth aspect of the present invention.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2002-088164    Patent Document 2: Japanese Patent Laid-Open Publication No. H08-302093    Patent Document 3: Japanese Patent Laid-Open Publication No. H07-076360    Patent Document 4: Japanese Patent Laid-Open Publication No. H11-349753    Patent Document 5: Japanese Patent Laid-Open Publication No. H08-302093    Patent Document 6: Japanese Patent Laid-Open Publication No. H08-113681    Patent Document 7: Japanese Patent Laid-Open Publication No. 2002-348417    Patent Document 8: Japanese Patent Laid-Open Publication No. 2005-47944    Patent Document 9: Japanese Patent Laid-Open Publication No. H08-269271    Patent Document 10: Japanese Patent Laid-Open Publication No. H09-278909    Patent Document 11: Japanese Patent Laid-Open Publication No. 2003-306587    Patent Document 12: Japanese Patent Laid-Open Publication 2002-234115    Patent Document 13: Japanese Patent Laid-Open Publication No. H08-302093    Patent Document 14: Japanese Patent Laid-Open Publication No. H06-198830    Patent Document 15: Japanese Patent Laid-Open Publication No. H06-16832    Patent Document 16: Japanese Patent Laid-Open Publication No. 2000-281807    Patent Document 17: Japanese Patent Laid-Open Publication No. H10-258488    Patent Document 18: Japanese Patent Laid-Open Publication No. 2003-313377    Patent Document 19: Unexamined Patent Application Publication No. H09-501447    Patent Document 20: Japanese Patent Laid-Open Publication No. H11-206406    Patent Document 21: Japanese Patent Laid-Open Publication No. 2001-171439    Patent Document 22: Japanese Patent Laid-Open Publication No. 2003-201375    Patent Document 23: Japanese Patent Laid-Open Publication No. 2000-91611    Patent Document 24: Japanese Patent Laid-Open Publication No. H08-283696    Patent Document 25: Japanese Patent Laid-Open Publication No. 2001-068703